"Turn-on-off" Fluorescent Probes Based on Carbon Nanoparticles for Hypochlorite and Fe²⁺ Detection

The identification of ClO^- and iron ions in water medium is a difficult task and has been one of the hot issues in analytical chemistry. For this objective, we synthesized carbon nanoparticles (CNPs) through a solvothermal reaction between 1, 3, 5-trimesic acid and o-phenylenediamine, which served as a sequential fluorescent probe for ClO^- and Fe²⁺ ions. The obtained CNPs were spherical particles with a diameter of 26.5 nm, exhibiting excellent fluorescence stability under a wide pH range, high ionic strength, and UV irradiation. Interestingly, the fluorescence of CNPs was selectively enhanced in the presence of ClO^-, and the resultant enhanced emission was extremely quenched by Fe²⁺. In view of this, a "turn-on-off" fluorescent probe was established, which possessed wonderful sensitivity and selectivity for quantitative analysis of ClO^- and Fe²⁺, with corresponding detection limits of 0.15 µM and 0.088 µM, respectively. In addition, the practicality and viability of the developed probe were validated by quantifying ClO^- and Fe²⁺ in tap water and river water.